The aerodynamic design of future aerospace vehicles will be greatly influenced by active flow control (AFC) technologies available for jet engine inlet and exhaust systems, aerodynamic surfaces including high-lift devices, thrust vectoring, weapons-bay cavity flow/acoustics, impingement jet noise reduction, and propulsion devices such as jet engines and rockets. These flow control systems will be used in a variety of flow situations to modify the shear layers and control mixing, energize the boundary layers to control flow separation, produce jet deflections to produce thrust vectoring and to control resonant cavity oscillations. An important aspect of the active flow control technology is the effective strategic deployment of suitable flow actuators. A variety of flow control actuators such as plasma-fluidic actuators, Powered Resonance Tubes (PRTs), piezoelectric actuators, synthetic jets, combustion-based flow actuators, blowing and suction holes, supersonic micro jets, and fluidic jets are currently being studied for flow control. These flow control actuators produce a steady, oscillating or pulsating acoustic, momentum or mass flow fields over a range of frequencies to affect the flow that is being controlled. Although most of these devices have demonstrated significant levels of flow control in laboratory scale experiments, integration of such systems into actual hardware of aerospace vehicles have remained a real challenge. These devices are required to operate under dynamic and harsh environments such as a wide range of temperatures, high levels of noise, vibration and shock loads as well as varying material stresses. Hence their performance should be robust, reliable with long, uninterrupted life cycle and should have a high degree of compatibility to be integrated with the system hardware.
While fluidic actuator oscillators are well known in the art, arranging them in a compact manner with common inlet manifolds to meet the demands of integration with airplane systems for application to flow control over the entire flight envelope (take-off, cruise and landing) is a challenging task and is an important feature of the present invention.
One such prior invention is described in Cerretelli et. al. (U.S. Pat. No. 7,128,082 B1) which is directed to the employment of a flow control system which includes an array of interconnected fluidic oscillators in a gas turbine engine and a gas turbine blade. Each fluidic oscillator in the array disclosed by Cerretelli et. al. carries an oscillating flow of the fluid and includes a throat, an input port connected to the throat, two control ports connected to the throat and two output or exit ports extending from the throat. Cerretelli et. al. fluidic oscillators are interconnected by shared feedback chambers and the exit ports produce pulsing jets in the same plane as the input flow for each fluidic oscillator in their array.
Another prior art invention directed to fluidic oscillators and their use in separation control is disclosed by Lucas et. al. (N. Lucas, 1. Taubert, R. Woszidlo, I. Wygnanski and M. A. Mc Veigh, “Discrete Sweeping Jets as Tool for Separation Control”, AIAA 2008-3868, presented at the 4th Flow Control Conference, Jun. 23-26, 2008, Seattle Wash.). Lucas et. al. disclose that a span wise line of discrete jets pointing in the direction of streaming and sweeping span wise provides effective flow control on various types of airfoils. Lucas et. al. disclose that their fluidic actuators produced frequencies of jet oscillations in the range of 0.3 to 1.2 kHz without disclosing the specific structure and design of the individual actuators, It is apparent from reading Lucas et. al. that the design of the fluidic actuator oscillators in their disclosed array are structurally and functionally different from the fluidic actuators of the present invention. For example, apparently each of the fluidic actuator oscillator designs that are relied upon and used in the arrays tested by Lucas et. al. have at least two input ports.
A compact array of independent, discrete or non-interconnected fluidic actuator oscillators is disclosed in the present invention each having a single input port which produces a single oscillating/sweeping or pulsing jet at each exit port for each fluidic actuator. When an exit pulsing jet is produced in the present invention it has a plane that may be typically perpendicular to the plane of the fluid flow inside the actuator. In the present invention each fluidic actuator oscillator in the array produces at the exit port an oscillating or sweeping jet of a much higher frequency than those previously used in prior art arrays, typically in the order of 1-22 kHz and with sweep angles between 20 to 120 degrees. An additional distinction over Cerretelli et. al. arrays is that their arrays cannot be manufactured in a single planar fashion because of the large volumes of the feedback paths or integrated with aerospace systems as easily as those of the present invention.